In cellular radio systems more wireless user equipment units (UEs) communicate via a radio access network to one or core networks. The user equipment can be a mobile telephone device, a laptop, a PDA or any other wireless device.
A radio access network covers a geographical area which is divided into cell areas. Each cell is served by at least one base station. A cell is defined as a geographical area where radio coverage is provided by the radio base station equipment at a base station site. Each cell is identified by a unique identity, which is broadcast in the cell. The base stations communicate over the air interface with the user equipment units (UE) within range of the base stations.
Recently, so called femto radio base stations have been introduced for use in a residential or small business environment. Such a residential or small business environment may constitute a local network. Femto base stations connect the local network to the service provider's core network via broadband (such as DSL or cable). A femto base station allows service providers to extend service coverage indoors, especially where access would otherwise be limited or unavailable. It incorporates the functionality of a typical base station but extends it to allow a simpler, self contained deployment, for example, a UMTS base station containing a NodeB, RNC and SGSN with Ethernet for backhaul.
A Gateway GPRS Support Node (GGSN) is a network node that acts as a gateway between a General Packetised Radio System (GPRS) wireless data network and other networks such as the Internet or private networks. The GGSN is the anchor point that enables the mobility of the user terminal in GPRS/UMTS networks. It maintains routing necessary to tunnel the protocol data units (PDUs) to the SGSN that service a particular mobile subscriber.The Radio Network Controller (RNC) is the governing element in the UMTS radio access network responsible for control of the NodeBs, i.e. the base stations which are connected to the controller.A Serving GPRS Support Node (SGSN) is responsible for the delivery of data packets from and to the mobile stations within its geographical service area. At the core network side an SGSN interfaces with one or more GGSNs. At the radio access network side the SGSN interfaces with an RNC.A nodeB is a logical network component of a UMTS radio access network responsible for radio transmission/reception in one or more cells to/from the user equipment. A nodeB interfaces with one or more user equipments within its coverage area and with an RNC at the network side.
Although for applying femto based radio stations much attention is focussed on UMTS, it is clear to any skilled person that the approach is readily applicable to all standards, including GSM, CDMA-2000, TD-SCDMA and WiMAX solutions. However, the problem tackled in the present invention is explained with a UMTS network as example.
UMTS femto base stations are small low cost, low power UMTS access points for home and corporate use cases. Mobile operators show a lot of interest in femto base station as a solution for improving indoor coverage as well as offloading traffic from the outdoor UMTS radio network. For the end-user, femto base stations offer the possibility to make cheap voice calls and data or multimedia sessions at home while using their regular cellular phone. Likewise for the mobile operator, femto base stations offer the possibility of offering high bandwidth end user services while offloading their main network.
Within the femto base station solution space, different implementations of a femto base station exist. The main difference between the different femto base station approaches lies in the mobile network functionality hosted on the residential base station and the corresponding degree to which the main network can be off-loaded.
A common characteristic of femto base stations is the fact that data exchanged between the mobile devices or sent towards fixed devices within the local network always passes through the mobile core network.
One way to achieve this is by tunneling all packet based end user data services over a GTP (GPRS Tunneling Protocol) tunnel from the femto base station at the residential side via a femto gateway (i.e. a network device residing in between the femto base stations and the mobile operators network and providing aggregation and security gateway functionality) to a SGSN or in some cases directly the GGSN in the mobile operator's core network. From both a technical and a business point of view this is a good approach for traffic sent to the Internet or to other end-users outside the own home or corporate environment. Furthermore it offers the potential of handovers between a femto base station and a macro cell, since the mobility anchor point resides in the mobile network (in the GGSN).
However for data being exchanged between a mobile device and a PC/laptop/set top box located within the same local network as the femto base station or between a mobile device and another mobile device connected to the femto base station this solution is both expensive and inefficient since all traffic must pass through the operator's core network prior to being routed back to the home. With mobile terminals getting more and more powerful and supporting a variety of multi-media applications the need for exchange and synchronization of data between home devices and mobile terminal increases and so a better solution is required in time.
Anchoring user traffic at two different places (local traffic in the home network and external traffic within the operator's core network) using a single IP address in the user equipment (UE) is currently not possible.
The GPRS specification allows a user to establish multiple ‘PDP context’ sessions with a single or multiple GGSNs. In this case each GGSN assigns a different IP address to the terminal out of its local address pool. The GGSN selection mechanism is based on APN (Access Point Names) specified by the UE during Packet Data Protocol (PDP) setup. With such a solution it is possible to locate one of the GGSN in the local network to handle local traffic. This solution however has multiple drawbacks:                1. A terminal needs to cope with multiple IP addresses, e.g. multi-homing problem of selecting the right IP address per application or peer node.        2. It is not transparent to the applications which IP address is to be used for which session. For IPv4, multiple IP addresses per terminal quickly leads to a shortage of public IPv4 addresses. This in its turn obliges the operator to assign private addresses, leading to well known issues with NAT (Network Address ‘and port’ Translation), like the introduction of Application Level Gateways.        3. The solution involves APN management. The end-user needs to explicitly request a PDP context towards a local GGSN, which is not transparent.        4. When a user handovers from his femto base station to an outdoor macro cell the local anchor point needs to be released. As such, handovers from femto base station to outdoor base station break the local sessions.        
Consequently, there is a need for an approach wherein these drawbacks of the prior art are overcome.